In a bistable display panel, the alternating current common voltages (AC Vcom) transition in each image frame may cause that pixels without the need of updating theirs display grey levels are mistakenly updated, resulting in the fading issue of display image.
FIG. 1 is a situation of display gray levels of pixels being mistakenly updated caused by the AC common voltage transition in the prior art. As depicted in FIG. 1, YDIO is a vertical start pulse input/output signal of each image frame, T is an image frame period, and Vcom is an AC common voltage. As seen from FIG. 1, in each image frame period T, the AC common voltage Vcom changes to a target voltage level at a time point that is at a half of the image frame period T. For example, in the first image frame period T of FIG. 1, the AC common voltage Vcom changes from a previous voltage level (e.g., −15V) to a target voltage level (e.g., +15V) and then is used as a target common voltage corresponding to the display data voltage in the first image frame period (i.e., current image frame period) T. Display data voltages (i.e., generally pixel data voltages) provided to pixels of the bistable display panel are generally set according to the target voltage level of AC common voltage Vcom in each image frame period, thereby determining whether to update the display grey levels of the respective pixels.
Specifically, as depicted in FIG. 1, in the first image frame period T, display data voltages respectively corresponding to a first gate line, a middle gate line and a last gate line represent that corresponding pixels are without the need of updating their display grey levels. In detail, with regard to the display data voltage corresponding to the middle gate line, because the time of which begins to be written into the corresponding pixel is synchronous with the transition of the AC common voltage Vcom and thus no voltage difference exists between the display data voltage and the AC common voltage Vcom, so that the original purpose of not updating its display gray level is achieved. However, as to the display data voltages respectively corresponding to the first and last gate lines, they have voltage differences with respect to the AC common voltage Vcom before and after transition respectively, so that the display gray levels of the corresponding pixels are mistakenly updated, resulting in the occurrence of fading issue in display image.